Many techniques are known for the production of hydrofluorocarbons (HFCs), and in particular difluoromethane (HFC-32). Certain prior methods involve fluorinating one or more chlorinated organic compounds to produce difluoromethane. The reaction product stream typically also contains byproducts and one or more unreacted starting materials. The desired difluoromethane is then recovered from the reaction product stream through one or more separation processes, such as distillation. For example, in certain difluoromethane production processes, a chlorinated organic compound, such as, for example, dichloromethane (HCC-30), and a fluorinating agent, such as, for example, hydrogen fluoride (HF), are reacted, usually after preheating, in the presence of a fluorination catalyst to generate a reaction product stream.
Distillation is well known in the art for separating the components of such reaction product streams and typically involves the use of distillation means, such as a packed column or one with trays, operated at pressures and temperatures selected to separate the reaction product stream into a stream relatively rich in the desired compound and stream relatively rich in compounds that are not desired in the finished product, such as unreacted components and unwanted byproducts. However, standard distillation techniques are generally ineffective to separate the components of azeotropic mixtures. Azeotropic binary compositions consisting of HFC-32 and chlorine are disclosed in U.S. Pat. No. 6,099,694, which is assigned to the assignee of the present invention and which is incorporated herein by reference.
The desirability of a fluorination process is generally linked to the yield and product purity resulting from the process. For example, if the desired product is the difluoromethane, the amount of such product which is recovered from the reaction product should ordinarily be as high as possible, and the type and amount of impurities contained in the final product stream should be as low as possible. While prior processes have achieved a certain level of success as measured by yield and product purity, applicants have discovered that that certain features of the prior art may raise barriers against continuing improvement of product yield and purity.